Battery Banter 4: Could the Grid Cope with a Next Generation EV?

In my last series of posts, I focussed on the war of attribution between electric vehicles (EVs) and traditional internal combustion engine vehicles (ICEs). Due to the recent slump in oil prices, EVs are on the defensive. They need increased volume to get down their cost curves and punch out of their current redoubt of super cars (Tesla) and green credential statement cars (Nissan Leaf). Low gasoline prices has made such an offensive a lot more tricky to pull off.

But let us suppose that a commercial super battery were to emerge that had high energy density and was cheap. What would happen next? Let’s run this thought experiment in a UK context.

First, let’s look a the UK’s existing fleet. Great Britain has a population of 64 million people, who between them drive around 29 million registered cars (source: here, click for larger image).

And annually each car is driven for an average of 8,000 miles, which translates into 22 miles per day (click for larger image; also remember we are smoothing out weekends and holidays).

From a previous blog post, I republish the following chart, which shows the kind of mileage per kilowatt-hour (kWh) a battery achieves at present.

Currently, the BMW i3 achieves around 5 miles per kWh. However, current generation EVs spend an awful lot of energy lugging around bloody great big batteries. With a super battery, like the lithium air batteries (li/O2) in the chart below (see my last post), you get four times as much energy for the same given weight. Let’s suppose that the auto makers double the battery capacity to get the required 200 mile range, but still halve the battery weight. Throw in even more use of modern materials and it is not unrealistic to guestimate that our future car would achieve 10 miles per kWh.

Using these numbers, 22 miles translates into 2.2 kWh per car. Next, we find the average number of cars per household in the UK, which is 1.1 (here, click for larger image). So we are looking at EV energy expenditure per household of about 2.4 kWh.

Meanwhile, average domestic daily electricity consumption per household in the UK is around, 4,200 kWh, which works out at 11.5 kWh per day (here, click for larger image).

We are now in a position to compare the daily EV energy expenditure of our hypothetical future household with current electricity consumption. In short, expending 2.4 kWh per day on the future EV will raise electricity consumption by 21% from the current level of 11.5 kWh. While that is a lot, it is not nearly as much as I would have originally thought.

5 responses to “Battery Banter 4: Could the Grid Cope with a Next Generation EV?”

I feel you’re being a little bullish on the benefits of battery weight reduction. Looking at some popular EVs: A Nissan Leaf has a 218kg battery in a 1,493kg car (Wikipedia). A Tesla Model S has a circa 550kg battery (Tesla Forums) in a 2,108kg car (Wikipedia). A BMW i3 has a 230kg battery (Telegraph) in a 1,315kg car (Wikipedia).

So an EV battery weighs between 15% and 25% of the total vehicle weight. Reducing the battery weight will therefore have a useful effect but I think that halving consumption might be a challenge even with extensive use of advanced materials elsewhere.

But even if you take a less bullish stance on EV demand your point still stands. At current rates of energy consumption a typical EV consumes less than a typical PV installation so vehicles parked at home during the day would largely be recharged by a domestic PV installation. For vehicles that are away from home more during the day, there’s plenty of off peak generation capacity to recharge them. We might well find people not bothering to plug in every night too. Why bother running your battery through a charge cycle when there’s still plenty in your battery for tomorrow’s driving?

I think there are some questions over the robustness of the distribution grid ad the DNOs will need to upgrade substations as EV penetration grows. But this can be mitigated as long as we can push people away from charging during peak times. Heat pumps will be a much bigger problem for the DNOs than EVs imo as they’ll be used at any time.

Another interesting question is what price point and cycle life would it take for grid balancing services and V2G to become viable for EV owners? It’s distinctly possible that we’ll be getting to that point in the not too distant future and then things will get really interesting.

Jamie. Thanks for the comments and point taken over the weight of the battery. I’m still trying to get my head around the weight by component breakdown of ICEVs and BEVs and how much is a function of intrinsic “carness” or intrinsic “powertrainness”. I have a couple of decent sources but not enough to work up into a blog post yet.